Quantifying Sources and Sinks of Rossby Wave Activity in the Atmosphere

量化大气中罗斯贝波活动的源和汇

• 批准号: 2154523
• 负责人: Noboru Nakamura
• 金额: $ 97.43万
• 依托单位: University of Chicago
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-04-01 至 2025-03-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2154523&HistoricalAwards=false
• 关键词: Quantifying; Sources; Sinks; Rossby; Wave

It is useful to think of the atmospheric circulation above the middle latitudes as a progression of waves, with alternating northward and southward air flow, superimposed on an eastward-flowing mean jet stream. The theory based on this wave-mean flow framework has been successful in explaining many aspects of the general circulation including the evolution of frontal weather systems and the effect of mountains on the upper-tropospheric flow. The Prpincipal Investigator (PI) has contributed to this theory by developing a measure of waviness which captures a trade-off in which wave activity increases at the expense of mean jet speed and vice versa, a consequence of the fluid analog of angular momentum conservation known as Kelvin's circulation theorem. The measure is called Finite Amplitude Wave Activity (FAWA), where finite amplitude refers to the fact that the measure can be used even when the waves distort the flow enough to create large circulation features which break off from the prevailing flow. FAWA represents the bulk wave activity around a latitude circle, and the PI has developed a related quantity called Local Wave Activity (LWA) to express waviness at each longitude along a latitude circle. Previous work by the PI's team has used the FAWA/LWA framework to explain the breakdown of the polar vortex during Sudden Stratospheric Warmings (SSWs) and the formation of blocking anticyclones (see AGS-1909522).The application of FAWA and LWA to problems like SSWs and blocking relies on their ability to capture interactions between waves and the eastward mean flow, which can be understood without knowing how the waves are generated or what eventually happens to them. But the generation and dissipation of wave activity are also represented in the evolution equations for FAWA and LWA, and the equations can be used to study wave sources and sinks and their role in atmospheric circulation. For example the dissipation of wave activity through diffusive mixing matters for the strength of the low-latitude meridional overturning cells (the Hadley cells), thus analysis of the sink term could offer insights into the expansion of the cells and the associated aridification seen in climate change simulations. Analysis of sources and sinks is promising but also challenging due to the need for intricate calculations involving small spatial scales and quantities which are hard to observe. Work under this award takes up the challenge, using a variety of techniques applied to idealized models, archived climate model output, and observational datasets (the ERA5 reanalysis in particular). Topics to be addressed through source/sink analysis include the seasonal cycle of wave activity, the role of the atmospheric boundary layer in generating and damping wave activity, and the generation of wave activity by condensational heating in convective clouds.The work has societal value due to the connection between upper-tropospheric waviness and surface weather, for instance blocking events are associated with extreme precipitation and SSWs can lead to severe cold air outbreaks. The software used to generate FAWA, LWA, and source/sink terms will be made openly available to the public via github, along with documentation on their use. Education and outreach are conducted through a biennial summer school and a local community science center. In addition, the project supports two graduate students and a postdoctoral fellow, thereby fostering the next generation of scientists in this research area.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

将中纬度地区上方的大气环流视为波浪的进展是有用的，其中有交替的向北和向南气流，叠加在向东流动的平均急流上。 基于波平均流框架的理论已经成功地解释了大气环流的许多方面，包括锋面天气系统的演变和山脉对对流层上层气流的影响。 首席研究员（PI）通过开发一种波纹度测量方法对这一理论做出了贡献，该测量方法捕获了一种权衡，其中波浪活动增加以牺牲平均射流速度为代价，反之亦然，这是已知角动量守恒的流体模拟的结果如开尔文循环定理。该措施被称为有限振幅波浪活动（FAWA），其中有限振幅是指即使波浪使水流扭曲到足以产生脱离主流水流的大环流特征，也可以使用该措施。 FAWA 表示纬度圈周围的体波活动，PI 开发了一个称为局域波活动 (LWA) 的相关量来表示沿纬度圈每个经度的波浪度。 PI 团队之前的工作使用 FAWA/LWA 框架来解释平流层突然变暖 (SSW) 期间极地涡旋的分解以及阻塞性反气旋的形成（参见 AGS-1909522）。FAWA 和 LWA 在以下问题中的应用SSW 和阻挡依赖于它们捕获波浪与向东平均流之间相互作用的能力，无需知道波浪如何产生或最终发生什么就可以理解这一点 他们。但波浪活动的产生和消散也体现在FAWA和LWA的演化方程中，这些方程可用于研究波浪源和汇及其在大气环流中的作用。 例如，通过扩散混合物质消散波浪活动，增强了低纬度经向翻转细胞（哈德来细胞）的强度，因此对汇项的分析可以深入了解细胞的扩张以及气候中所见的相关干旱化改变模拟。 对源和汇的分析是有前景的，但也具有挑战性，因为需要进行复杂的计算，涉及小空间尺度和难以观察的数量。 该奖项的工作迎接了这一挑战，使用了应用于理想化模型、存档气候模型输出和观测数据集（特别是 ERA5 再分析）的各种技术。 通过源/汇分析要解决的主题包括波浪活动的季节周期、大气边界层在产生和抑制波浪活动中的作用以及对流云中的凝结加热产生波浪活动。这项工作具有社会价值，因为考虑到对流层上层波浪与地面天气之间的联系，例如阻塞事件与极端降水有关，而南海风则可能导致严重的冷空气爆发。 用于生成 FAWA、LWA 和源/汇术语的软件及其使用文档将通过 github 向公众公开。 教育和推广是通过两年一次的暑期学校和当地社区科学中心进行的。此外，该项目还支持两名研究生和一名博士后研究员，从而培养该研究领域的下一代科学家。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查进行评估，认为值得支持标准。